The invention relates to an apparatus for measuring the contents of foreign matters in a flowing liquid, in particular a buoyant apparatus, which has a housing where at least one wall section is to be brought into contact with the liquid, and exhibits a preferably spherical arched outer side and a sensor in a hole for the foreign matter, the outer side of which in the area of the hole is permeable to the foreign matters that are to be measured, and flushes with the arched outer side of the wall section.
An apparatus of this kind is known from GB 2 005 421 A. It serves to analyze wastewater, in particular for the measurement of the oxygen content. Besides, it can be used to measure nutrient solutes in the water, e.g. nitrates and phosphates. The housing has the form of a hollow ball, which is manufactured with two diametrically opposing holes in a rotational injection moulding process. A through-going pipe is adhered to the holes, and a further pipe incorporating the sensor screwed into it is inserted to an extent, that its outer side formed by a front end diaphragm flushes with the outer side of the housing. The diaphragm is also essentially arched in a ball shape. The ball-shaped form of the housing and the arching of the diaphragm gives the advantage, that a flowing liquid, in which the apparatus is partly immersed or is floating, is kept free from contaminations, for example fouling or an oil film, and thus will not impair or destroy the measuring ability of the sensor.
The object of the invention is to achieve an apparatus of the already described type where the velocity of the liquid is increased further in the area of the outer side of the sensor which is in contact with the liquid.
According to the invention, the object is reached in that the arched outer side of the wall section has guiding surfaces for the liquid extending transversely to the hole.
Due to the the guiding surfaces the liquid flow is concentrated on the arched outer side of the mentioned wall section of the housing and, consequently, on the outer side of the sensor which has the diaphragm, and its flow velocity is increased. In this way, the risk of a contamination of the diaphragm is further reduced.
Preferably, it is arranged, that the guiding surfaces extend radially to the hole. By this design, the liquid flow will be led relatively precise over the centre of the diaphragm.
Further, the guiding surfaces can be arranged around the hole at equal angular distances. In this way, the liquid flow is led over the diaphragm even if it is somewhat tilted in relation to the guiding surfaces.
Principally, the guiding surfaces can be made by the side walls of slots. Preferably they are, however, constructed by means of thin walls which project from the outer side of the wall section. These walls require less material and ensure an essentially laminar flow, as long as they extend in the flow direction.
The free edge of the walls can be arched to the outer side whereby their flow resistance remains low, as long as they extend in the direction of flow.
The outer arched wall section of the housing can be detachably connected with the other part of the housing.
The detachable connection enables a quick assembly and if necessary a quick replacement of the sensor.
The detachable connection could be constructed as a screw connection. It is, however, preferably constructed as a bajonet socket which makes it possible particularly quick to loosen, respectively connect, the arched wall section of the housing with the rest of the housing part.